The specific objective is to determine he effect of dose protraction on the biological effectiveness of low energy neutrons, where the endpoint is oncogenic transformation. For fission spectrum neutrons and high LET charged particles we have demonstrated the existence of an inverse dose-rate effect for transformation, i.e., the biological effect of a given dose increase as the dose-rate in reduced. The effect is significant only for certain combinations of dose, dose-rate and the LET of radiation involved. It is usually assumed that protracted exposures are less effective than acute exposure by a factor of at least 2. There is evidence that for some neutron energies and some charged particles the opposite is true, i.e., that protracted exposures are more effective that acute exposure. This project, therefore, has important implications in radiation protection.